Negative results

[supertobi]

If I place a PV left from the selected building I get negativ values. This should not be possible:

[FlorianK13]

Hi @supertobi, thanks for the report.
It seems like it is still possible to draw PV systems on Buildings that were not simulated. Not allowing PV systems there should be the way to go.

[FlorianK13]

Equivalent to #294